Friction Bite with Swellable Elastomer Elements

ABSTRACT

A friction-enhancing material is applied to an outer surface of a swellable element of a downhole tool. The friction-enhancing material helps prevent axial extrusion of the elastomer of the swellable element. The friction-enhancing material may include particles, a mesh, and wickers, among other kinds of friction-enhancing material, and may be disposed on or embedded in all or a portion of an outer surface of the swellable element.

TECHNICAL FIELD

The present invention relates to the field of downhole tools, and inparticular to swellable packers.

BACKGROUND ART

In the field of hydrocarbon exploration and production, various toolsare used to provide fluid seals between two components in a wellboreAnnular barriers have been designed for preventing undesirable flow ofwellbore fluids in the annulus between a wellbore tubular and the innersurface of a surrounding tubular or the borehole wall. In many cases,the annular barriers provide a fluid seal capable of holding asignificant pressure differential across its length. In one application,a wellbore packer is formed on the outer surface of a completion stringthat is run into an outer casing in a first condition having aparticular outer diameter. When the packer is in its desired downholelocation, it is inflated or expanded into contact with the inner surfaceof the outer casing to create a seal in the annulus. Similar wellborepackers have been designed for use in openhole environments, to create aseal between a tubular and the surrounding wall of the wellbore.

Conventional packers are actuated by mechanical or hydraulic systems. Aforce or pressure is applied from the wellhead to move a mechanicalpacker element radially into contact with the surrounding surface. In aninflatable packer, fluid is delivered from the wellhead to inflate achamber defined by a bladder around the tubular body.

More recently, wellbore packers have been developed which include amantle of swellable material formed around the tubular. The swellablematerial is selected to increase in volume on exposure to at least onepredetermined fluid, which may be a hydrocarbon fluid or an aqueousfluid or brine. The swellable packer may be run to a downhole locationin its unexpanded state, where it is exposed to a wellbore fluid andcaused to increase in volume. The design, dimensions, and swellingcharacteristics are selected such that the swellable packer elementexpands to create a fluid seal in the annulus to isolate one wellboresection from another. Swellable packers have several advantages overconventional packers, including passive actuation, simplicity ofconstruction, and robustness in long-term isolation applications.

In addition, swellable packers may be designed for compliant expansionof the swellable mantle into contact with a surrounding surface, suchthat the force imparted on the surface prevents damage to a rockformation or sandface, while still creating an annular barrier or seal.Swellable packers therefore lend themselves well to openhole completionsin loose or weak formations.

The materials selected to form a swellable element in a swellable packervary depending on the specific application. Swellable materials areelastomeric (i.e. they display mechanical and physical properties of anelastomer or natural rubber). Where the swellable mantle is designed toswell in hydrocarbons, it may comprise a material such as an ethylenepropylene diene monomer (EPDM) rubber. Where the swellable mantle isrequired to swell in aqueous fluids or brines, the material for examplemay comprise an N-vinyl carboxylic acid amide-based cross-linked resinand a water swellable urethane in an ethylene propylene rubber matrix.In addition, swellable elastomeric materials may be designed to increasein volume in both hydrocarbon fluids and aqueous fluids.

One failure mode of packing elements that seal in an annular space isextrusion. Mechanical backups have been used to bridge off the extrusiongap and help retain the swellable packing element, but these are notalways practical or possible.

SUMMARY OF INVENTION

In one embodiment, a downhole apparatus is disclosed. The downhole toolcomprises a swellable element. The swellable element comprises aswellable elastomeric material selected to increase in volume onexposure to at least one predetermined fluid; and a first area, disposedwith the swellable element and operable to increase friction between theswellable element and a surrounding surface upon swelling of theswellable element.

In another embodiment, a swellable element for a downhole tool isdisclosed. The swellable element comprises a swellable elastomericmaterial selected to increase in volume on exposure to at least onepredetermined fluid; and a friction-enhancing material, disposed on afirst annular area of an outer surface of the swellable elastomericmaterial.

In yet another embodiment, a method of reducing axial extrusion of aswellable element of a downhole tool is disclosed. The method comprisesdisposing a friction-enhancing material on a portion of an outer surfaceof the swellable element.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an implementation of apparatusand methods consistent with the present invention and, together with thedetailed description, serve to explain advantages and principlesconsistent with the invention. In the drawings,

FIG. 1 is a cutaway view of a downhole tool according to one embodiment.

FIG. 2 is a cutaway view of a downhole tool according to anotherembodiment.

FIG. 3 is a cutaway view of a downhole tool according to yet anotherembodiment.

DESCRIPTION OF EMBODIMENTS

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the invention. It will be apparent, however, to oneskilled in the art that the invention may be practiced without thesespecific details. In other instances, structure and devices are shown inblock diagram form in order to avoid obscuring the invention. Referencesto numbers without subscripts or suffixes are understood to referenceall instance of subscripts and suffixes corresponding to the referencednumber. Moreover, the language used in this disclosure has beenprincipally selected for readability and instructional purposes, and maynot have been selected to delineate or circumscribe the inventivesubject matter, resort to the claims being necessary to determine suchinventive subject matter. Reference in the specification to “oneembodiment” or to “an embodiment” means that a particular feature,structure, or characteristic described in connection with theembodiments is included in at least one embodiment of the invention, andmultiple references to “one embodiment” or “an embodiment” should not beunderstood as necessarily all referring to the same embodiment.

FIG. 1 is a cutaway view of a portion of a swellable packer 100according to one embodiment. Some common features of the swellablepacker known to the art are omitted for clarity of the drawing. Theswellable packer 100 comprises a central body 110, such as a tubular ormandrel, about which is disposed a swellable elastomer mantle 120. Theswellable mantle 120 may be formed of one or more sections as desired,using any known technique for forming a swellable mantle about a centralbody. In one embodiment, the swellable mantle 120 may be bonded orotherwise attached to the body 110. The swellable mantle 120 is formedof an elastomer designed to swell when exposed to an aqueous solution,such as water or brine, or a hydrocarbon fluid.

Upon insertion into the well, the elastomer of the mantle 120 swellsupon exposure to the fluid surrounding the packer 100 in the wellbore.As the elastomer of the mantle 120 swells, it expands radiallyoutwardly, engaging a surrounding casing or open hole wellbore (notshown in FIG. 1) sealing the packer 100 in an annular space around thepacker 100, typically to the casing or wellbore. The elastomer of themantle 120 may also swell axially, and if not prevented from doing so,may extrude axially around the other elements disposed at the ends ofthe mantle 120, reducing the pressure that is exerted by the expandedmantle 120 on the surrounding casing or wellbore.

To prevent this extrusion, mechanical backup units 130 may be provided.Axial expansion of the mantle 120 is limited by the backup units 130,which typically expand under axial pressure, reducing extrusion aroundthe expanded backup units. Although backup units 130 are disposed atboth ends of the swellable mantle 120 as illustrated in FIG. 1, in someembodiments, the backup unit 130 may be disposed at only one end of themantle 120, or a different technique for reducing extrusion may beemployed at the end of the mantle 120 axially distal from the backupunit 130. Although mechanical backups 130 have been used to bridge offthe extrusion gap and help retain the swellable packing element, theseare not always practical or possible. Furthermore, some extrusion mayoccur around the backup units 130.

By increasing the friction factor between the mantle 120 and the bore,the extrusion resistance is increased, and thus the pressure holdingcapability of the packer 100. Various embodiments disclosed herein useimplanted mechanical components disposed on or embedded into the outersurface of the swellable mantle 120 to increase the friction or grippingcapability of the mantle 120. These mechanical components may includeparticles, slip segments, wire-mesh sheet, etc. that would either biteinto the bore, or provide a rougher, stronger surface than the swellablerubber. These mechanical components may increase the tensile holdingcapability of the element, as well as increasing the pressure holdingcapability of the packer 100.

There are different ways of increasing the friction coefficient of thesurface of the mantle 120. In FIG. 1, the friction enhancement isachieved by disposing particles 140 onto the outer surface of the mantle120, or embedding the particles 140 into the outer surface. Theparticles 140 provide an increased friction coefficient for the entiresurface of the mantle 120. As illustrated in FIG. 1, the particles 140are randomly distributed across the surface of the mantle 120. In otherembodiments, the particles 140 may be randomly distributed across one ormore portions of the outer surface of the mantle 120, preferably atleast in areas proximal to the ends of the mantle 120, where extrusionof the elastomer around the backup units 130 may occur.

In yet other embodiments, the friction-enhancing particles 140 may bepatterned across the entire or portions of the outer surface of themantle 120, using any desired pattern.

The friction increasing particles 140 in one embodiment may comprisecarbide particles, designed to bite into the surrounding surface of thecasing or wellbore. Other friction-enhancing particles 140 may be usedthat are not hard enough to bite into the surrounding surface, but whichadd frictional improvement to the mantle 120, such as elastomers orplastic particles that are harder than the elastomer forming the mantle120.

The particles 140 may be of any desired size, and the density ofdistribution of the particles 140 may be any desired density. Theparticles 140 may be deposited on or embedded into the elastomer of themantle 120 before disposition of the mantle 120 on the body 110, or maybe added after the mantle 120 is disposed on the downhole tool 100.

In an alternate embodiment, instead of using particles 140 added to theouter surface of the mantle 120, the outer surface of the mantle 120 maybe scored or roughened mechanically producing random or patternedscorings or roughened areas to increase the friction coefficient of thesurface of the mantle 120.

FIG. 2 is a cutaway view of a downhole tool 200 according to oneembodiment in which, instead of discrete particles 140, a mesh 240 isdisposed about the mantle 120 to provide friction enhancement. The mesh240 may be formed of wire, such as a stainless steel wire, or any otherdesired materials. As with the embodiment of FIG. 1, the mesh 240 may beformed of the material hard enough to bite into the surrounding surfaceof the casing or wellbore, but may alternately simply be harder than theelastomer used to form the mantle 120. The mesh 240 may be disposed onthe outer surface of the mantle 120 or may be embedded into the surfaceof the mantle 120.

FIG. 3 is a cutaway view of a downhole tool 300 according to yet anotherembodiment. In this embodiment, one or more areas of wickers 340 may bedisposed annularly about the outer diameter of the mantle 120 to providethe desired friction enhancement. As illustrated in FIG. 3, six areas ofwickers 340 are provided, but the number and placement of the wickerareas 340 is illustrative and by way of example only. Any number ofwicker areas 340 may be placed in any desired arrangement on the mantle120. Preferably, wicker areas 340 are placed proximal to the ends of themantle 120 where extrusion around backup units 130 may occur.

The wickers may be formed of stainless steel or any other material. Inone embodiment, the wickers may be formed of a material of sufficienthardness to bite into the surrounding surface. In another embodiment,the wickers do not need to be hard enough to bite into the surroundingsurface, but simply are harder than the mantle 120, thus increasefrictional drag on the mantle 120.

The wickers may have any desired shape configured to increased friction,and do not need to be capable of anchoring the mantle 120 to completelyprevent movement of the mantle 120 relative to the surrounding surface.

Although as described above the friction-enhancing material is disposedon the outer surface of the mantle 120, and other embodiments thefriction-enhancing elements, whether separate particles, meshes,wickers, or other forms, may be embedded into the elastomer of themantle 120 below the outer surface. Under pressure from the expandedmantle 120 against the surrounding surface, the subsurface embeddedfriction-enhancing elements may, instead of directly engaging thesurrounding surface to resist movement, pinch the elastomer of themantle 120 between the friction-enhancing elements 140, 240, or 340,enhancing friction between the mantle 120 and the surrounding surface.

By increasing friction between the mantle 120 and the surroundingsurface, the friction-enhancing elements 140, 240, and 340 reduce axialextrusion of the elastomer of the mantle 120 around the supportassemblies or backup rings 130 disposed at the ends of the mantle 120.By reducing extrusion, the pressure on the surrounding surface caused bythe expansion of the elastomer radially outwardly may be increased.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments may be used in combination with each other. Many otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. The scope of the invention therefore should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled. In the appendedclaims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein.”

1. A downhole apparatus, comprising: a swellable element comprising aswellable elastomeric material selected to increase in volume onexposure to at least one predetermined fluid; and a first area, disposedwith the swellable element and operable to increase friction between theswellable element and a surrounding surface upon swelling of theswellable element.
 2. The downhole apparatus of claim 1, wherein thedownhole apparatus is a swellable packer.
 3. The downhole apparatus ofclaim 1, wherein the first area comprises a plurality of particlesdisposed on a surface of the first area, the particles selected forfriction enhancement.
 4. The downhole apparatus of claim 3, wherein theplurality of particles are dispersed randomly on the surface of thefirst area.
 5. The downhole apparatus of claim 3, wherein the pluralityof particles are patterned onto the surface of the first area.
 6. Thedownhole apparatus of claim 1, wherein the first area comprises a meshdisposed about an outer diameter of the first area, the mesh selectedfor friction enhancement.
 7. The downhole apparatus of claim 6, whereinthe mesh is composed of stainless steel wire.
 8. The downhole apparatusof claim 1, wherein the first area comprises a plurality of wickers,formed of material selected for friction enhancement.
 9. The downholeapparatus of claim 1, wherein the first area comprises a plurality ofwickers, formed of material selected to be harder than the surroundingsurface.
 10. The downhole apparatus of claim 1, wherein the first areacomprises: a roughened radially outward surface of a portion of theswellable element.
 11. The downhole apparatus of claim 1, wherein thefirst area comprises the entire outer surface of the swellable element.12. The downhole apparatus of claim 1, further comprising: a backupmember, configured to resist axial extrusion of the swellable element,disposed at an end of the swellable element.
 13. The downhole apparatusof claim 12, wherein the first area is proximal to the backup member.14. A swellable element for a downhole tool, comprising: a swellableelastomeric material selected to increase in volume on exposure to atleast one predetermined fluid; and a friction-enhancing material,disposed on a first annular area of an outer surface of the swellableelastomeric material.
 15. The swellable element of claim 14, wherein thefriction-enhancing material comprises a plurality of particles disposedon the outer surface of the first annular area.
 16. The swellableelement of claim 15, wherein the plurality of particles are formed froma material selected to have a hardness sufficient to bite into asurrounding surface when deployed in a casing or wellbore.
 17. Theswellable element of claim 15, wherein the plurality of particles arerandomly dispersed in the first annular area.
 18. The swellable elementof claim 15, wherein the plurality of particles are patterned on thefirst annular area.
 19. The swellable element of claim 14, wherein thefriction-enhancing material comprises a mesh, disposed about an outerdiameter of the first annular area.
 20. The swellable element of claim14, wherein the friction-enhancing material comprises a plurality ofwickers, disposed about an outer diameter of the first annular area. 21.The swellable element of claim 14, wherein the predetermined fluid is anaqueous solution.
 22. A method of reducing axial extrusion of aswellable element of a downhole tool, comprising: disposing afriction-enhancing material on a portion of an outer surface of theswellable element.
 23. The method of claim 22, wherein the act ofdisposing a friction-enhancing material comprises: disposing particlesof a substance harder than the swellable element on the portion of theouter surface of the swellable element.
 24. The method of claim 22,wherein the act of disposing a friction-enhancing material comprises:disposing a plurality of wickers about the portion of the outer surfaceof the swellable element.
 25. The method of claim 22, wherein the act ofdisposing a friction-enhancing material comprises: disposing a meshformed of a substance harder than the swellable element about theportion of the outer surface of the swellable element.
 26. The method ofclaim 22, wherein the act of disposing a friction-enhancing materialcomprises: embedding the friction-enhancing material into the portion ofthe outer surface of the swellable element.